Backing discs for rotary sanders and the like are formed of limitedly flexible material for carrying abrasive material and numerous improvements have been developed including the provision of ridges or ribs to control disc rigidity and assist in cleaning and cooling abrasive sheet material on the disc. A recent major advance in this field is disclosed and claimed in the U.S. Pat. No. 3,974,598 wherein particularly oriented blades direct sanded particles in a single direction from a work piece operated upon by the disc.
The present invention comprises an improvement in the fan disc of U.S. Pat. No. 3,974,598. One of the major advantages of the above-noted fan disc is the capability for use on portable equipment wherein the backing disc is operated out in the open without any type of hood or cover and yet sanded particles are discharged in a single predetermined direction. While this result is truly amazing, it is noted that the vanes or blades on the backing disc are exposed during disc rotation. It is thus possible for an operator to inadvertently touch one or more vanes. Although proper handling of a portable sander, for example, should preclude an operator from touching the vanes on the back of the disc, it is possible for mistakes to occur with damaging results to the operator. Rotary sanders and the like normally operate at high speed, so that an operator who inadvertently places a finger tip or knuckle, for example, too close to the back of the disc may be injured. It is also noted that the blades on the back surface of this type of disc limit the flexibility of the disc and this may be disadvantageous in at least certain circumstances.